LEAD ARSENATE. 325 



Allowing for the variations in process of manufacture, it 

 would seem, however, that the content of arsenic oxide in the 

 various commercial lead arsenates was conditioned more by the 

 wetness of the material than anything else; the content of water 

 in the sariiples analysed ranged from 33.65 to 58.44 per cent. 

 A perfectly dry material 'has not been found advantageous, for 

 while even in such a form it remains in suspension several times 

 as long as the -finest Paris green, it settles about three times as 

 fast as w^hen the arsenate is used in the form of a paste. On 

 the other hand, the paste must not be too tenacious or it will be 

 difficult to break up and distribute evenly throughout the spray- 

 ing mixture. Colby* has found this objection to hold with 

 Disparene. In making the water-soluble determinations it was 

 observed that there were marked variations in the rate of settling 

 even when the samples were in the dry and powdered condition. 

 It is probable that the same peculiarity would have been noted 

 in the samples in their original state, but as in most cases the 

 whole sample had already been dried, verification of this sup- 

 fMDsition was impossible. 



HOME-MADE LEAD ARSENATE. 



It has frequently been recommended that farmers prepare 

 their own lead arsenate as they need it. Colbyf recommends 

 the following formula: Dissolve 24 oz. of lead acetate or 20 oz. 

 of lead nitrate in one gallon of cold water; also separately dis- 

 solve ID oz. sodium arsenate in thi%e quarts of water, both 

 solutions to be made in wooden vessels. Pour the separate 

 solutions into the spray tank containing from 100 to 150 gallons 

 of water ; a white precipitate of lead arsenate immediately forms. 

 This preparation may be made several times stronger without the 

 least danger of injury to the foliage. The freshly precipitated 

 home-made arsenate seems to keep in suspension better than 

 even the best commercial preparations. 



COST OF LEAD ARSENATE. 



As stated before, only one of the samples was bought in the 

 open market; the prices have therefore not been affixed in any 

 case. By correspondence with the manufacturers the Station 



* California Expt. Station, Bull. 151. 

 I Loc. cit. 



